There are conventionally known devices for measuring a cylinder stroke position by detecting an amount of rotation of a rotary roller using a rotation sensor.
FIG. 1(A) conceptually shows a structure of a rotation sensor forming a cylinder stroke position measurement device.
As shown in FIG. 1(A), a rotating shaft 6000 is rotatably supported by a fixing member 2000 through a bearing or the like. A rotor 3000 is provided at one end of the rotation shaft 1000. The rotor 3000 has a magnet 4000 arranged thereon such that a magnetic flux density is periodically varied according to a rotational position of the rotor. A rotary roller 1000 is provided at the other end of the rotating shaft 6000 by means of a joint or the like. The rotary roller 1000 is arranged so as to be in contact with a surface of a piston rod 7000 sliding within a cylinder. The rotary roller 1000 is arranged so as to rotate according to translational movement of the rod 7000.
A magnetic sensor section 5000 is provided at a position opposing the rotor 3000 in the axial direction of the rotating shaft 6000. The magnetic sensor section 5000 detects a magnetic flux density generated by the magnet 4000 and outputs an electrical signal according to the magnetic flux density. The electrical signal detected by the magnetic sensor section 5000 is converted from the amount of rotation of the rotary roller 1000 into an amount of displacement of the rod 7000 by a processing unit downstream thereof.
The rotary roller 1000 of the rotation sensor as described above must be pressed against the rod surface by means of a pressing member in order to prevent slip between the rotary roller 1000 and the rod 7000.
Patent Document 1 mentioned below describes an invention in which a rotary roller is pressed against a cylinder rod by means of a spring.
FIGS. 1(B) and 1(C) show a structure of a rotation sensor described in the Patent Document 1.
As shown in FIGS. 1(B) and 1(C), a lid 7200 is provided on a cylinder outer tube 7100. The lid 7200 has a frame 7300 attached thereto. The frame 7300 has a lever 7400 rotatably attached thereto. The lever 7400 has a rotary roller 1000 rotatably attached thereto. The rotary roller 1000 is in contact with the surface of a rod 7000 so as to rotate in accordance with displacement of the rod 7000.
A spring 7500 is interposed between the rotary roller 1000 and the lid 7200 such that the spring 7500 presses the rotary roller 1000 against the surface of the rod 7000. Thus, a rotation sensor unit 9000 is constituted by the lid 7200, the frame 7300, the lever 7400, the rotary roller 1000, and the spring 7500.
The lid 7200 forms a part of the outer tube 7100. The lid 7200 is mounted on an opening of the outer tube 7100. As a result, the components forming the rotation sensor unit 9000 is accommodated between the outer tube 7100 and the rod 7000. The rotary roller 1000 is pressed against the rod surface by the spring force of the spring 7500.
Patent Document 2 mentioned below describes a stroke sensor for measuring a displacement position of a rod, in which a magnetic sensor is mounted on a cylinder head while magnetic scales are embedded in various parts in the axial direction of the rod, so that a magnetic field generated by the magnetic scales is detected by means of the magnetic sensor.
Patent Document 1: Japanese Patent No. 2957570
Patent Document 2: Japanese Patent Application Laid-Open No. 2000-234603